The present invention is directed to a Bragg cell spectral analyzer with a prism expansion system for the expansion of a laser beam being conducted to the Bragg cell. The laser beam emerges from an opening, which has a diameter lying in the order of magnitude of a millimeter, as a parallel bundle of light which has a Gaussian cross-sectional distribution of the light intensity and the beam is supplied in this form to the expansion system. Stray light may be superimposed on the emerging parallel bundle of light.
An analyzer of a type having a prism expansion system is disclosed in Optical Engineering, Vol. 16, No. 5, Sept./Oct. 1977, pp. 461-466. In the disclosed analyzer, the laser beam is so greatly expanded by the expansion system that the half-width value of the Gaussian cross-section distribution of the intensity, which is assumed as ideal, is of approximately the same size as the aperture of the Bragg cell. The frequency resolution of the Bragg cell is fully utilized by means of the specific Gaussian apodization. However, on the other hand, a spectrum still has relatively high diffraction fringes where side lobes will occur. The relationship of the height or intensity of these diffraction side lobes relative to the height or intensity of the principal maximum of the spectrum defines the dynamic range of the analyzer. With the diffraction side lobes being lower in comparison to the principal maximum, the dynamic range is all the greater.